/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/PreviewMesh.h
Get the entire materials array from the preview mesh. Appends to OutMaterials without clearing it.
void GetMaterials ( [TArray](API\Runtime\Core\Containers\TArray)< [UMaterialInterface](API\Runtime\Engine\Materials\UMaterialInterface) * > & OutMaterials ) const